The present invention relates to absorbent materials. More specifically, the invention relates to a reinforced networked polymer/clay alloy composite useful, for example, in containment applications such as landfill liners or covers, reservoir liners, underground storage tank liners, secondary containment liners, and man-made bodies of water, or personal care absorbent articles, including diapers, training pants, feminine hygiene products such as sanitary napkins, incontinence devices and the like.
There are a number of commercial applications for absorbent materials, including, without limitation, in containment applications as landfill liners or covers, reservoir liners, underground storage tank liners, secondary containment liners, and man-made bodies of water, or personal care absorbent articles, including diapers, training pants, feminine hygiene products such as sanitary napkins, incontinence devices and the like. While the applications are diverse, there is need for a material having improved water absorbency and/or fluid barrier properties.
For example, in waste containment applications, hydraulic barriers can reduce the escape or leakage of harmful leachates into surface and ground waters. In man-made bodies of water, a hydraulic barrier acts to contain the water within an enclosure or defined impoundment area.
In one type of liner, hydraulic barriers are often formed from bentonite. Specifically, bentonite is admixed with the soil forming the water-holding area. Upon contact of the bentonite with water, the bentonite swells and thereby fills up the voids found in the soil. However, the water absorption capacity of bentonite alone may not be sufficient for the containment of some water-soluble wastes.
U.S. Pat. No. 3,949,560 (Clem, Apr. 13, 1976) is directed to a soil sealant composition dry mixed with soil. The soil sealant composition consists of bentonite, a water-soluble dispersing agent and a pre-formed water-soluble polymer. The water-soluble dispersing agent is a phosphoric acid salt, sulfate of ROSO3X (R is a C8-C32 hydrocarbon, X is an alkaline metal or ammonium) or a leonardite salt. The pre-formed water-soluble polymer is polyacrylic acid, water-soluble salts of polyacrylic acid, hydrolyzed poly-acrylonitrile, polyvinyl acetate, polyvinyl alcohol, copolymers of the foregoing or a copolymer of acrylic acid and maleic anhydride. A water containing enclosure is formed from the soil/soil sealant mixture and contacted with water to hydrate the bentonite. The resulting hydrated enclosure is used for containing water contaminated with industrial waste. No reinforcing agent is used with the soil/soil sealant mixture.
U.S. Pat. No. 4,048,373 (Clem, Sep. 13, 1977), U.S. Pat. No. 4,103,499 (Clem, Aug. 1, 1978) and U.S. Pat. No. 4,139,588 (Clem, Feb. 13, 1979) all describe a water barrier panel or moisture impervious panel comprised of a soil sealant sandwiched between two paperboard sheets. More particularly, the panel is formed of a corrugated paperboard carrier or form including a pair of spaced paperboard facing sheets interconnected by a paper corrugated strip to form a plurality of voids. The voids are filled with the soil sealant composition described in U.S. Pat. No. 3,949,560 and the edges of the panel may be sealed with wax, tape or water-soluble gum. When contacted with water, moisture passes through the paperboard sheets to the soil sealant composition, where the bentonite swells.
More recently, so-called geosynthetic clay liners (xe2x80x9cGCLxe2x80x9d) have become relatively widely accepted for use as hydraulic barriers. A GCL has a layer of bentonite supported by a geotextile or a geomembrane material, mechanically held together by needling, stitching or chemical adhesives.
An example of a GCL prepared with a chemical adhesive is provided in U.S. Pat. No. 4,467,015 (Clem, Aug. 21, 1984). This patent describes a waterproofing structure or water impervious sheet material comprised of layers of flexible carrier sheets coated with a water swellable composition. The water swellable composition is clay or a dry granular mixture of clay, a pre-formed water-soluble polymer, such as polyacrylic acid, and a water-soluble salt. The composition is secured by using an adhesive, whether water-soluble or -insoluble or a solvent-soluble or -insoluble adhesive. A disadvantage of this type of laminate is that clays in the GCL may still migrate away from the GCL with the leachate percolating through the liner, albeit very slowly.
Similarly, U.S. Pat. No. 4,810,573 (Harriet, Mar. 7, 1989) describes a laminated composite article with a clay composition adhered to a water-impermeable sheet. The clay composition is an intimate mixture of water swellable clay and a pre-formed elastomer, such as polypropylene and/or polybutene. The intimate clay/elastomer mixture is produced by blending clay with pre-formed elastomers in a sigma blender to masticate the elastomer. The clay composition is adhered to the water-impermeable sheet by rolling to form a laminate. U.S. Pat. No. 5,580,630 (Byrd, Dec. 3, 1996) describes a multi-layer article using the same clay composition as Harriet.
As indicated above, rather than using a chemical adhesive, the layers of the GCL may be mechanically held together by other means such as stitching and needle punching. For instance, U.S. Pat. No. 4,565,468 (Crawford, Jan. 21, 1986) described a moisture impermeable barrier comprised of two fabric layers quilted together. A top sheet member is positioned over a base sheet member having a layer of bentonite resting on its upper surface. The top sheet member is secured to the base sheet member by stitches extending therebetween. The stitching forms either quilted compartments or elongated corrugated compartments containing the bentonite therein.
DE 3704503 A1 (Heerten et al.) discloses an article having two fabric layers sandwiching a bentonite clay layer, wherein the two fabric layers are needle punched together. U.S. Pat. No. 5,174,231 (White, Dec. 29, 1992) describes a multi-layer article including an intermediate layer of a water-swellable colloidal clay sandwiched between two layers of flexible material or fabric sheet. The two layers are structurally interconnected through the intermediate clay layer such as by needle punching, sewing, quilting, or needle looming, to interconnect fibers of one fabric layer to the other fabric layer at spaced locations over essentially the entire surface areas of both layers.
Thus, in these GCLs, the clay particles are either adhered onto the geotextile or geomembrane or are physically confined by opposing layers of geotextile or geomembrane. The opposing layers of geotextile or geomembranes are mechanically held together by means such as sewing, quilting and needle punching, which limits the movement of clay particles therebetween. However, the clay particles in granular bentonite used in these applications are typically a couple of micrometers or less in diameter. Further, the void spaces in the geotextiles or geomembranes and the spacing of the stitching or needle punching tend to be greater than the size of the clay articles. Thus, it is still possible for the clay particles in the GCL to migrate out of the liner, particularly when placed under a hydraulic pressure gradient, albeit slowly.
It is commonly known that bentonite swells well in fresh water but poorly in, water containing salts and/or metals, such as saltwater, seawater, acid mine drainage, and the like. Thus, while GCL""s are effective barriers for fresh water, they are ineffective barriers to water with high salt and dissolved metals concentrations.
Another problem with GCL""s is that the bentonite is typically dry and, therefore, until the bentonite swells, waste water can flow through the GCL. Accordingly, GCL""s must first be pre-hydrated after installation. This pre-hydration step can take up to 48 hours, for example.
Yet another problem with GCL""s is their weight. Typically, a GCL weighs more than 5 kg/M2. Because of its weight, transportation and installation costs are significant.
Accordingly, there is a need for an absorbent material for containment applications, especially environmental containment applications, which is salt water and contaminant resistant. Also, there is a need for a barrier liner that is lighter than GCL, but having substantially comparable or improved barrier properties versus GCL. Moreover, there is a need for an absorbent material having intimately integrated components that do not disperse and/or migrate from the product, particularly when exposed to or immersed in water, and can effectively absorb water containing salt and/or metals.
According to the invention, there is provided a process for producing a reinforced networked polymer/clay alloy composite, comprising the steps of: (a) preparing a monomer/clay mixture by mixing at least a monomer, clay particles, a cross-linking agent, and a mixing fluid in a vessel; (b) contacting the monomer/clay mixture and a reinforcing agent; (c) exposing the monomer/clay mixture to a polymerization initiator means; and (d) polymerizing the monomer/clay mixture in the presence of the reinforcing agent so that a reinforced networked polymer/clay alloy composite is formed.
According to the invention, there is also provided a product produced by the process described above.
According to the invention, there is further provided a reinforced networked polymer/clay alloy composite comprising a networked polymer/clay alloy, wherein the alloy is a chemically integrated composition of polymer and clay, and the alloy is intimately integrated with a reinforcing agent so that, when the composite is immersed in deionized water, at a temperature in a range of from about 20xc2x0 C. to about 30xc2x0 C., the alloy swells with substantially no clay separating from the composite.
According to the invention, there is provided the method of using the reinforced networked polymer/clay alloy composite as an absorbent material for a personal care product or as a fluid barrier in a confining stress range of from about 0 kPa to about 10000 kPa, wherein, when placed under a zero confining stress, the barrier has a deionized water flux less than about 1xc3x9710xe2x88x928 m3/m2/s.